This invention relates generally to master cylinders for vehicle braking systems and more specifically to an end cap for retaining the piston actuating mechanism within the master cylinder.
Vehicle braking systems have long employed various configurations of a master cylinder. The master cylinder transforms the mechanical travel of a brake pedal in a vehicle to fluid pressure which is then transmitted via brake lines to brake drums or disc brakes at the wheels of a vehicle. Generally, a brake pedal when depressed by an operator causes a translation of a mechanical linkage. The mechanical linkage extends from the passenger compartment of the vehicle to most commonly the engine compartment. The mechanical linkage engages one end of the brake system master cylinder. The master cylinder is generally comprised of a reservoir mounted atop a master cylinder housing. The master cylinder housing has one or two inlets for supplying brake fluid at atmospheric pressure to the master cylinder piston actuating mechanism. As the brake pedal is depressed, the linear translation of the linkage causes the piston actuating mechanism to translate within the master cylinder housing. The translation of the piston actuating mechanism results in an increase in the fluid pressure which is in turn transmitted to the individual brakes at the wheels for braking the vehicle.
While the concept of mechanically translating a piston to transform linear motion into increased fluid pressure has been understood for many years and is the basic principal in the operation of braking system master cylinders throughout the vehicle industry, the specific construction of individual master cylinders are relatively complex and involve a large number of components. These large numbers of components comprising a master cylinder assembly further requires that the individual parts be manufactured to fine tolerances to minimize the degree of travel of the brake pedal before braking becomes effective. Typically, master cylinders include both a primary and a secondary piston, which are arranged in an in-line configuration. Such a configuration generally results in a final assembly that is relatively long. Newer vehicles include a power braking system wherein the master cylinder is coupled to a vacuum booster to minimize the amount of pressure a vehicle operator must place on the brake pedal to accomplish effective braking of the vehicle. The vacuum booster further adds to the length of the assembly.
As motor vehicles have evolved over the years and especially recently, engine compartments are becoming smaller while at the same time there are an ever increasing number of engine accessories and components which must be located within the engine compartment. Consequently, minimization of the overall size of the combination vacuum booster and master cylinder assembly has become highly desirable. Various means for reducing the assembly size have been incorporated including having at least a portion of the master cylinder assembly extending into the vacuum booster.
While such designs have helped to alleviate the space problem within the engine compartment, they have also contributed to the increased complexity in the design of the master cylinder. Specifically, the portion of the master cylinder that extends into the vacuum booster, is commonly called the boot nose portion of the master cylinder. The boot nose portion of the master cylinder also includes the opening to the internal cavity of the master cylinder whereby the piston actuating mechanism is inserted. Once the piston actuating mechanism is inserted into the master cylinder it must be retained therein in such a manner that it will withstand the linear pressures exerted by the pressurized brake fluid when the braking system is actuated. Until now, the most common method for retaining the piston actuating mechanism within the master cylinder is with a bearing socket. As shown in FIG. 2, illustrating one embodiment of the prior art, the boot nose portion 24 of a master cylinder housing 22 defines an internal cavity 23. The piston actuating mechanism 21 is inserted into cavity 23 and is retained therein with a bearing socket 29. Bearing socket 29 incorporates a large diameter fine-machined thread about its outer periphery, which is threaded into matching internal threads in the boot nose portion 24 of the master cylinder housing 22.
Such a configuration wherein a bearing socket incorporates large diameter fine threads to be threaded into matching threads in the boot nose of the master cylinder results in substantial complexity and cost in the manufacture of the master cylinder components. In addition to the increased cost of manufacturing the large diameter threads, there is a corresponding difficulty in assembling two components with large diameter fine threads. Large diameter fine threads increase the probability that when the two parts are mated, the parts can be axially misaligned thus resulting in cross threading of the bearing socket into the boot nose. Such cross-threading results in undesired scrapping of precision machined components, thus adding unnecessary expense to the manufacturing process. Thus, there is a need in the industry for a mechanism by which the precision-machined parts can be properly mated and aligned while minimizing the manufacturing cost and providing for ease of assembly.
One aspect of the present invention is a master cylinder for vehicle braking systems. The master cylinder includes a housing having a central cavity with at least one fluid supply inlet port and at least one pressure outlet port. The housing also has a flange at one end thereof. A piston actuation mechanism is housed within the central cavity and is moveable between a first position wherein the central cavity is in fluid communication with the fluid supply inlet and a second position wherein the central cavity is in fluid communication with the pressure outlet. A cup-shaped end cap is fastened to the housing flange in a fluid sealing relationship. The cup-shaped end cap receives at least a portion of the piston actuation mechanism and retains the piston actuation mechanism in an operational configuration within the housing.
Another aspect of the present invention is a cup-shaped end cap for retaining a piston actuation mechanism within a master cylinder housing. The end cap comprises a tubular body having a wall defining a central cavity for receiving a portion of the piston actuating mechanism therein and a bottom at one end of the body. A flange extends peripherally outward from the body at an opposite end wherein the flange defines a central opening for receiving the piston actuation mechanism of a master cylinder. The flange further comprises a resilient seal on at least one face thereof.
These and other features, advantages, and objectives of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.